Discovery and inspiration of large-and medium-sized glutenite-rich oil and gas fields in the eastern South China Sea:An example from Paleogene Enping Formation in Huizhou 26 subsag,Pearl River Mouth Basin

Based on the practice of oil and gas exploration in the Huizhou Sag of the Pearl River Mouth Basin,the geochemical indexes of source rocks were measured,the reservoir development morphology was restored,the rocks and minerals were characterized microscopically,the measured trap sealing indexes were compared,the biomarker compounds of crude oil were extracted,the genesis of condensate gas was identified,and the reservoir-forming conditions were examined.On this basis,the Paleogene Enping Formation in the Huizhou 26 subsag was systematically analyzed for the potential of oil and gas resources,the development characteristics of large-scale high-quality conglomerate reservoirs,the trapping effectiveness of faults,the hydrocarbon migration and accumulation model,and the formation conditions and exploration targets of large-and medium-sized glutenite-rich oil and gas fields.The research results were obtained in four aspects.First,the Paleogene Wenchang Formation in the Huizhou 26 subsag develops extensive and thick high-quality source rocks of semi-deep to deep lacustrine subfacies,which have typical hydrocarbon expulsion characteristics of"great oil generation in the early stage and huge gas expulsion in the late stage",providing a sufficient material basis for hydrocarbon accumulation in the Enping Formation.Second,under the joint control of the steep slope zone and transition zone of the fault within the sag,the large-scale near-source glutenite reservoirs are highly heterogeneous,with the development scale dominated hierarchically by three factors(favorable facies zone,particle component,and microfracture).The(subaqueous)distributary channels near the fault system,with equal grains,a low mud content(<5%),and a high content of feldspar composition,are conducive to the development of sweet spot reservoirs.Third,the strike-slip pressurization trap covered by stable lake flooding mudstone is a necessary condition for oil and gas preservation,and the NE and nearly EW faults obliquely to the principal stress have the best control on traps.Fourth,the spatiotemporal configuration of high-quality source rocks,fault transport/sealing,and glutenite reservoirs controls the degree of hydrocarbon enrichment.From top to bottom,three hydrocarbon accumulation units,i.e.low-fill zone,transition zone,and high-fill zone,are recognized.The main area of the channel in the nearly pressurized source-connecting fault zone is favorable for large-scale hydrocarbon enrichment.The research results suggest a new direction for the exploration of large-scale glutenite-rich reservoirs in the Enping Formation of the Pearl River Mouth Basin,and present a major breakthrough in oil and gas exploration.

Characteristics of carbon isotopic composition of alkane gas in large gas fields in China

Exploration and development of large gas fields is an important way for a country to rapidly develop its natural gas industry.From 1991 to 2020,China discovered 68 new large gas fields,boosting its annual gas output to 1925×108m3in 2020,making it the fourth largest gas-producing country in the world.Based on 1696 molecular components and carbon isotopic composition data of alkane gas in 70 large gas fields in China,the characteristics of carbon isotopic composition of alkane gas in large gas fields in China were obtained.The lightest and average values ofδ^(13)C_(1),δ13C2,δ13C3andδ13C4become heavier with increasing carbon number,while the heaviest values ofδ^(13)C_(1),δ13C2,δ13C3andδ13C4become lighter with increasing carbon number.Theδ^(13)C_(1)values of large gas fields in China range from-71.2‰to-11.4‰(specifically,from-71.2‰to-56.4‰for bacterial gas,from-54.4‰to-21.6‰for oil-related gas,from-49.3‰to-18.9‰for coal-derived gas,and from-35.6‰to-11.4‰for abiogenic gas).Based on these data,theδ^(13)C_(1)chart of large gas fields in China was plotted.Moreover,theδ^(13)C_(1)values of natural gas in China range from-107.1‰to-8.9‰,specifically,from-1071%o to-55.1‰for bacterial gas,from-54.4‰to-21.6‰for oil-related gas,from-49.3‰to-13.3‰for coal-derived gas,and from-36.2‰to-8.9‰for abiogenic gas.Based on these data,theδ^(13)C_(1)chart of natural gas in China was plotted.

Two highly efficient accumulation models of large gas fields in China

Based on reserve abundance,large gas fields in China can be divided into two types：type one of high abundance large gas fields,dominated by structural gas reservoirs; type two of low abundance large gas fields,dominated by stratigraphic and lithologic gas reservoirs.The formation of these two types of large gas fields is related to the highly efficient accumulation of natural gas.The accumulation of high abundance gas fields is dependent on the rapid maturation of the source kitchen and huge residual pressure difference between the gas source kitchen and reservoir,which is the strong driving force for natural gas migration to traps.Whereas the accumulation of low abundance gas fields is more complicated,involving both volume flow charge during the burial stage and diffusion flow charge during the uplift stage,which results in large area accumulation and preservation of natural gas in low porosity and low permeability reservoirs.This conclusion should assist gas exploration in different geological settings.

Formation and distribution characteristics of Proterozoic–Lower Paleozoic marine giant oil and gas fields worldwide

There are rich oil and gas resources in marine carbonate strata worldwide.Although most of the oil and gas reserves discovered so far are mainly distributed in Mesozoic,Cenozoic,and upper Paleozoic strata,oil and gas exploration in the Proterozoic–Lower Paleozoic（PLP）strata—the oldest marine strata—has been very limited.To more clearly understand the oil and gas formation conditions and distributions in the PLP marine carbonate strata,we analyzed and characterized the petroleum geological conditions,oil and gas reservoir types,and their distributions in thirteen giant oil and gas fields worldwide.This study reveals the main factors controlling their formation and distribution.Our analyses show that the source rocks for these giant oil and gas fields are mainly shale with a great abundance of type I–II organic matter and a high thermal evolution extent.The reservoirs are mainly gas reservoirs,and the reservoir rocks are dominated by dolomite.The reservoir types are mainly karst and reef–shoal bodies with well-developed dissolved pores and cavities,intercrystalline pores,and fractures.These reservoirs arehighly heterogeneous.The burial depth of the reservoirs is highly variable and somewhat negatively correlated to the porosity.The cap rocks are mainly thick evaporites and shales,with the thickness of the cap rocks positively correlated to the oil and gas reserves.The development of high-quality evaporite cap rock is highly favorable for oil and gas preservation.We identified four hydrocarbon generation models,and that the major source rocks have undergone a long period of burial and thermal evolution and are characterized by early and long periods of hydrocarbon generation.These giant oil and gas fields have diverse types of reservoirs and are mainly distributed in paleo-uplifts,slope zones,and platform margin reef-shoal bodies.The main factors that control their formation and distribution were identified,enabling the prediction of new favorable areas for oil and gas exploration.

Effect of HCO_3^- concentration on CO_2 corrosion in oil and gas fields

The effect of HCO3^- concentration on CO2 corrosion was investigated by polarization measurement of potentiodynamic scans and weight-loss method, Under the conditions of high pressure and high temperature, the corrosion rate of steel X65 decreased with the increase of HCO3^- concentration, while pH of solution increased. SEM, EDS, and XRD results of the corrosion scales indir cated that the typical FeCO3 crystallite was found at low HCO3^- concentration but Ca（Fe,Mg）（CO3）2 was found at high HCO3^- con- centration. Ca^2＋ and Mg^2＋ are precipitated preferential to Fe^2＋ at high pH value. Potentiodynamic polarization curves showed that the cathodic current density decreases with the increase of HCO3^- concentration at low HCO3^- concentration. When the HCO3^- concentration reaches 0.126 mol/L, increasing HCO3^- concentration promotes cathodic reactions. Anodic behavior is an active process at low HCO3^- concentration and the anodic current density decreases with the increase of HCO3^- concentration. An evident active-passive behavior is exhibited in anodic process at 0.126 mol/L HCO3^-.

Gas source of the Middle Jurassic Shaximiao Formation in the Zhongjiang large gas field of Western Sichuan Depression:Constraints from geochemical characteristics of light hydrocarbons

The Zhongjiang gas field is a typical large gas field in terrigenous strata of the Western Sichuan Depression.It remains debatable which member of the Upper Triassic Xujiahe Formation served as the source rocks and how significant the member contributed to the gas accumulations in the Zhongjiang gas field.In this study,we analyzed the essential characteristics of the Lower Jurassic source rocks and the geochemical features of light hydrocarbons in natural gas from the 2nd(T_(3)χ^(2))and 4th members(T_(3)χ^(4))of the Upper Triassic Xujiahe Formation(T_(3)χ),as well as the Middle Jurassic Shaximiao(J_(2)s)and Qianfoya(J_(2)q)formations.Based on this,we explored the sources of the natural gas in the Zhongjiang gas field and determined the natural gas migration patterns and their effects on the properties of light hydrocarbons in the natural gas.The results indicate that the Lower Jurassic lacustrine source rocks of the Zhongjiang gas field contain humic organic matter,with vitrinite reflectance(R_(0))values ranging from 0.86%to 0.98%.Samples meeting the criterion for effective source rocks[total organic carbon(TOC)content≥0.75%]exhibited an average TOC content of merely 1.02%,suggesting significantly lower hydrocarbon generation potential than source rocks in the underlying T3x,which show higher thermal maturity and TOC contents.For natural gas samples from T_(3)χ^(2),T_(3)χ^(4),J_(2)s,and J_(2)q reservoirs,their C_(5-7)iso-alkane content was significantly higher than their n-alkane content,and their methylcyclohexane(MCH)index ranged from 59.0%to 77.3%,indicating the predominance of methylcyclohexane in C_(7)light hydrocarbons.As indicated by the origin identification and gas-source correlation based on the geochemical features of light hydrocarbons,the natural gas in the Zhongjiang gas field is typical coal-derived gas.The gas from the primary pay zone of the Shaximiao Formation,with significantly high K_(1),(P_(2)+N_(2))/C_(7),and P_(3)/C_(7)values,predominantly originated from the 5th member of the T3x and migrated in the free phase,with a small amount possibly sourced from the Lower Jurassic source rocks.The dissolution and adsorption during gas migration led to a decrease in the aromatic content in C_(6-7)light hydrocarbons and an increase in the isoheptane values.Therefore,their effects must be considered when determining the gas origin and thermal maturity based on the aromatic content in C_(6-7) light hydrocarbons and iso-heptane values.

Stress corrosion cracking behavior of buried oil and gas pipeline steel under the coexistence of magnetic field and sulfate-reducing bacteria

Magnetic field and microorganisms are important factors influencing the stress corrosion cracking(SCC)of buried oil and gas pipelines. Once SCC occurs in buried pipelines, it will cause serious hazards to the soil environment. The SCC behavior of X80 pipeline steel under the magnetic field and sulfate-reducing bacteria(SRB) environment was investigated by immersion tests, electrochemical tests, and slow strain rate tensile(SSRT) tests. The results showed that the corrosion and SCC sensitivity of X80 steel decreased with increasing the magnetic field strength in the sterile environment. The SCC sensitivity was higher in the biotic environment inoculated with SRB, but it also decreased with increasing magnetic field strength, which was due to the magnetic field reduces microbial activity and promotes the formation of dense film layer. This work provided theoretical guidance on the prevention of SCC in pipeline steel under magnetic field and SRB coexistence.

Tracing of natural gas migration by light hydrocarbons:A case study of the Dongsheng gas field in the Ordos Basin,NW China

Based on the analysis of light hydrocarbon compositions of natural gas and regional comparison in combination with the chemical components and carbon isotopic compositions of methane,the indication of geochemical characteristics of light hydrocarbons on the migration features,dissolution and escape of natural gas from the Dongsheng gas field in the Ordos Basin is revealed,and the effect of migration on specific light hydrocarbon indexes is further discussed.The study indicates that,natural gas from the Lower Shihezi Formation(Pix)in the Dongsheng gas field displays higher iso-C5-7contents than n-C5-7contents,and the C6-7light hydrocarbons are composed of paraffins with extremely low aromatic contents(<0.4%),whereas the C7light hydrocarbons are dominated by methylcyclohexane,suggesting the characteristics of coal-derived gas with the influence by secondary alterations such as dissolution.The natural gas from the Dongsheng gas field has experienced free-phase migration from south to north and different degrees of dissolution after charging,and the gas in the Shiguhao area to the north of the Borjianghaizi fault has experienced apparent diffusion loss after accumulation.Long-distance migration in free phase results in the decrease of the relative contents of the methylcyclohexane in C7 light hydrocarbons and the toluene/n-heptane ratio,as well as the increase of the n-heptane/methylcyclohexane ratio and heptane values.The dissolution causes the increase of isoheptane values of the light hydrocarbons,whereas the diffusion loss of natural gas in the Shiguhao area results in the increase of n-C5-7contents compared to the iso-C5-7contents.

Distribution and exploration direction of medium-and large-sized marine carbonate gas fields in Sichuan Basin, SW China

Based on the analysis of the basic characteristics of medium-and large-sized marine gas fields in Sichuan Basin, combined with the division of major reservoir forming geological units in the marine craton stage and their control on key hydrocarbon accumulation factors, the distribution law of medium-and large-sized marine carbonate gas fields in the basin was examined and the exploration direction was pointed out. Through the analysis of the periodic stretching-uplifting background, it is concluded that five large scale paleo-rifts, three large scale paleo-uplifts, five large scale paleo erosion surfaces were formed in the marine craton stage of Sichuan Basin, and these geological units control the key reservoir forming factors of medium and large sized gas fields:(1) Large-scale paleo-rifts control the distribution of high-quality hydrocarbon generation centers.(2) The margin of large-scale paleo-rifts, high position of paleo-uplifts and paleo erosion surfaces control the distribution of high-quality reservoirs.(3) Large-scale paleo-rifts, paleo-uplifts, paleo erosion surfaces and present tectonic setting jointly control the formation of many types of large and medium-sized traps.(4) Natural gas accumulation is controlled by the inheritance evolution of traps in large geological units. Based on the comparative analysis of the distribution characteristics of medium-and large-sized gas fields and large geological units, it is proposed that the superimposition relationship between single or multiple geological units and the present structure controls the distribution of medium-and large-sized gas fields, and the "three paleo" superimposed area is the most advantageous. According to the above rules, the main exploration fields and directions of medium-and large-sized marine carbonate gas fields in Sichuan Basin include periphery of Deyang-Anyue paleo-rift, eastern margin of Longmenshan paleo-rift, margins of Kaijiang-Liangping oceanic trough and Chengkou-western Hubei oceanic trough, the high part of the subaqueous paleo-uplifts around Central Sichuan, paleo erosion surfaces of the top boundary of Maokou Formation in eastern and southern Sichuan Basin, paleo erosion surfaces of the top boundary of the Leikoupo Formation in central and western Sichuan Basin.

Electrical structure identification of deep shale gas reservoir in complex structural area using wide field electromagnetic method

To fully exploit the technical advantages of the large-depth and high-precision artificial source electromagnetic method in the complex structure area of southern Sichuan and compensate for the shortcomings of the conventional electromagnetic method in exploration depth,precision,and accuracy,the large-depth and high-precision wide field electromagnetic method is applied to the complex structure test area of the Luochang syncline and Yuhe nose anticline in the southern Sichuan.The advantages of the wide field electromagnetic method in detecting deep,low-resistivity thin layers are demonstrated.First,on the basis of the analysis of physical property data,a geological–geoelectric model is established in the test area,and the wide field electromagnetic method is numerically simulated to analyze and evaluate the response characteristics of deep thin shale gas layers on wide field electromagnetic curves.Second,a wide field electromagnetic test is conducted in the complex structure area of southern Sichuan.After data processing and inversion imaging,apparent resistivity logging data are used for calibration to develop an apparent resistivity interpretation model suitable for the test area.On the basis of the results,the characteristics of the electrical structure change in the shallow longitudinal formation of 6 km are implemented,and the transverse electrical distribution characteristics of the deep shale gas layer are delineated.In the prediction area near the well,the subsequent data verification shows that the apparent resistivity obtained using the inversion of the wide field electromagnetic method is consistent with the trend of apparent resistivity revealed by logging,which proves that this method can effectively identify the weak response characteristics of deep shale gas formations in complex structural areas.This experiment,it is shown shows that the wide field electromagnetic method with a large depth and high precision can effectively characterize the electrical characteristics of deep,low-resistivity thin layers in complex structural areas,and a new set of low-cost evaluation technologies for shale gas target layers based on the wide field electromagnetic method is explored.

Coupling mechanism of THM fields and SLG phases during the gas extraction process and its application in numerical analysis of gas occurrence regularity and effective extraction radius

The analysis of the coupling mechanism of thermal-hydraulic-mechanical(THM)fields,and solid-liquidgas(SLG)phases during gas extraction process is of profound significance to explore its numerical application in the gas occurrence regularity and its effective extraction radius.In this study,the Hudi coal mine in Qinshui basin is taken as the research area,the influencing factors of gas occurrence were analyzed,the differences in overburden load for gas pressure distribution and the factors influencing the effective extraction radius were further discussed by using the COMSOL software.The results show that the derivation of mathematical model in gas extraction shows that the process is a process the THM fields restrict each other,and the SLG phases influence each other.The longer the extraction time,the larger the influencing range of borehole,and the better the extraction effect.The larger the diameter of borehole,the larger the effective extraction radius,and the influence on gas extraction effect is smaller in the early stage and larger in the late stage.The borehole arrangement should be flexibly arranged according to the actual extraction situation.The higher the porosity,the higher the permeability,the better the gas extraction effect.The larger the overburden load of reservoir,the stronger the effective stress,which will result in the more severe the strain,and the closure of pore and fracture,which in turn will lead to the decrease of permeability and slow down the gas extraction.The relationship among extraction time,borehole diameter,negative pressure of gas extraction,permeability with effective extraction radius is exponential.This study has important theoretical and practical significance for clarifying and summarizing the gas occurrence regularity and its engineering practice.

Formation of overpressure system and its relationship with the distribution of large gas fields in typical foreland basins in central and western China

Based on the data of measured formation pressure, drilling fluid density of key exploration wells and calculated pressure by well logging, combined with the analysis of natural gas geological conditions, the characteristics and formation mechanisms of formation fluid overpressure systems in different foreland basins and the relationship between overpressure systems and large-scale gas accumulation are discussed.(1) The formation mechanisms of formation overpressure in different foreland basins are different. The formation mechanism of overpressure in the Kuqa foreland basin is mainly the overpressure sealing of plastic salt gypsum layer and hydrocarbon generation pressurization in deep–ultra-deep layers, that in the southern Junggar foreland basin is mainly hydrocarbon generation pressurization and under-compaction sealing, and that in the western Sichuan foreland basin is mainly hydrocarbon generation pressurization and paleo-fluid overpressure residual.(2) There are three common characteristics in foreland basins, i.e. superimposed development of multi-type overpressure and multi-layer overpressure, strong–extremely strong overpressure developed in a closed foreland thrust belt, and strong–extremely strong overpressure developed in a deep foreland uplift area.(3) There are four regional overpressure sealing and storage mechanisms, which play an important role in controlling large gas fields, such as the overpressure of plastic salt gypsum layer, the overpressure formed by hydrocarbon generation pressurization, the residual overpressure after Himalayan uplift and denudation, and the under-compaction overpressure.(4) Regional overpressure is an important guarantee for forming large gas fields, the sufficient gas source, large-scale reservoir and trap development in overpressure system are the basic conditions for forming large gas fields, and the overpressure system is conducive to forming deep to ultra-deep large gas fields.

Efficient development strategies for large ultra-deep structural gas fields in China

Through analyzing the development of large ultra-deep structural gas fields in China,strategies for the efficient development of such gas fields are proposed based on their geological characteristics and production performance.According to matrix properties,fracture development degree and configuration between matrix and fractures,the reservoirs are classified into three types:single porosity single permeability system,dual porosity dual permeability system,and dual porosity single permeability system.These three types of gas reservoirs show remarkable differences in different scales of permeability,the ratio of dynamic reserves to volumetric reserves and water invasion risk.It is pointed out that the key factors affecting development efficiency of these gas fields are determination of production scale and rapid identification of water invasion.Figuring out the characteristics of the gas fields and working out pertinent technical policies are the keys to achieve efficient development.The specific strategies include reinforcing early production appraisal before full scale production by deploying high precision development seismic survey,deploying development appraisal wells in batches and scale production test to get a clear understanding on the structure,reservoir type,distribution pattern of gas and water,and recoverable reserves,controlling production construction pace to ensure enough evaluation time and accurate evaluation results in the early stage,in line with the development program made according to the recoverable reserves,working out proper development strategies,optimizing pattern and proration of wells based on water invasion risk and gas supply capacity of matrix,and reinforcing research and development of key technologies.

Exploration of Complicated Oil and Gas Fields

Complicated oil and gas fields occupy an important position in oil and gas exploration. In this paper, complicated oil and gas fields are grouped into four types: fault-block, lithologic, stratigraphic and fissure types. On the basis of the new theory of petroleum geological exploration in composite oil and gas accumulation areas within continental basins, a new exploration sequence suitable for complicated oil and gas fields has been established, which comprises four stages:(1) initial exploration;(2) preliminary exploration;(3) early step-by-step exploration and development: and(4) late step-by-step exploration and development. The idea of cybernetics has been taken to control various links of a systematic exploration project so as to fully, effectively and comprehensively utilize the new exploration techniques, eventually realizing the optimization of exploration with the aim of raising the efficiency of exploration of complicated oil and gas fields.

North slope transition zone of Songnan-Baodao sag in Qiongdongnan Basin and its control on medium and large gas fields,South China Sea

Based on analysis of newly collected 3D seismic and drilled well data,the geological structure and fault system of Baodao sag have been systematically examined to figure out characteristics of the transition fault terrace belt and its control on the formation of natural gas reservoirs.The research results show that the Baodao sag has the northern fault terrace belt,central depression belt and southern slope belt developed,among them,the northern fault terrace belt consists of multiple transition fault terrace belts such as Baodao B,A and C from west to east which control the source rocks,traps,reservoirs,oil and gas migration and hydrocarbon enrichment in the Baodao sag.The activity of the main fault of the transition belt in the sedimentary period of Yacheng Formation in the Early Oligocene controlled the hydrocarbon generation kitchen and hydrocarbon generation potential.From west to east,getting closer to the provenance,the transition belt increased in activity strength,thickness of source rock and scale of delta,and had multiple hydrocarbon generation depressions developed.The main fault had local compression under the background of tension and torsion,giving rise to composite traps under the background of large nose structure,and the Baodao A and Baodao C traps to the east are larger than Baodao B trap.Multiple fault terraces controlled the material source input from the uplift area to form large delta sand bodies,and the synthetic transition belt of the west and middle sections and the gentle slope of the east section of the F12 fault in the Baodao A transition belt controlled the input of two major material sources,giving rise to a number of delta lobes in the west and east branches.The large structural ridge formed under the control of the main fault close to the hydrocarbon generation center allows efficient migration and accumulation of oil and gas.The combination mode and active time of the main faults matched well with the natural gas charging period,resulting in the hydrocarbon gas enrichment.Baodao A transition belt is adjacent to Baodao 27,25 and 21 lows,where large braided river delta deposits supplied by Shenhu uplift provenance develop,and it is characterized by large structural ridges allowing high efficient hydrocarbon accumulation,parallel combination of main faults and early cessation of faulting activity,so it is a favorable area for hydrocarbon gas accumulation.Thick high-quality gas reservoirs have been revealed through drilling,leading to the discovery of the first large-scale gas field in Baodo 21-1 of Baodao sag.This discovery also confirms that the north transition zone of Songnan-Baodao sag has good reservoir forming conditions,and the transition fault terrace belt has great exploration potential eastward.

Dewatering Techniques for Gas Recovery in Sichuan Gas Fields

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Petroleum Geology in the Tarim，Junggar and Turpan－Hami Basins Showing Favorable Conditions for the OccurrenceofLargeandMediumoilandGasFields

The frequent upwarping and subsidence,and folding and uplifting of the earth crust caused by the isostatic adjustments and tectonic movements change the types of sediments in the basins frequently,and often cause the occurrence of multi-source formations in the geologic profile.As in the Tarim basin,during the first transgression in the early paleozoic,the deepest location was the Ordovician sag,in which deep marine clastic and carbonate rocks were deposited and main source rocks were included.In the late Paleozoic,it was the second transgression cycle,the thickest sedi-ments of Carboniferous-Permian were deposited in thie Awati sag and southwest sag which would be another major petroleum source rocks(Fig.2).

Correlation between per-well average dynamic reserves and initial absolute open flow potential(AOFP) for large gas fields in China and its application

Based on performance data of over 600 wells in 32 large gas fields of different types in China, the correlation is established between per-well average dynamic reserves( G) and average initial absolute open flow potential(IAOFq) of each field, and its connotation and applicability are further discussed through theoretical deduction. In log-log plot, G vs. IAOFq exhibit highly dependent linear trend, which implicates the compatibility between G and IAOFq attained through development optimization to reach the balance among annual flow capacity, maximum profits and certain production plateau, that is to match productivity with rate maintenance capacity. The correlation can be used as analogue in new gas field development planning to evaluate the minimum dynamic reserves which meet the requirement of stable and profitable production, and facilitate well pattern arrangement. It can also serve as criteria to appraise the effectiveness and infill drilling potential of well patterns for developed gas fields.

Development characteristics, models and strategies for overseas oil and gas fields

Based on about 20 years of accumulated experience and knowledge of oil and gas field development in overseas countries and regions for China's oil companies, the development features, ideas, models and plan designing strategies of overseas oil and gas fields were comprehensively summarized. Overseas oil and gas field development has ten major features, such as non-identity project resource, diversity of contract type, complexity of cooperation model, and so on. The overseas oil and gas field development aims at the maximization of production and benefit during the limited contract period, so the overseas oil and gas field development models are established as giving priority to production by natural energy, building large-scale production capacity, putting into production as soon as possible, realizing high oil production recovery rate, and achieving rapid payback period of investment. According to the overseas contract mode, a set of strategies for overseas oil and gas field development plans were made. For tax systems contracts, the strategy is to adopt the mode of "first fat and then thinner, easier in the first and then harder", that is, early investment pace, production increase rate, development workload and production were decided by the change of tax stipulated in the contract. For production share contracts, the strategy is to give priority to high production with a few wells at a high production recovery rate to increase the cost-oil and shorten the period of payback. For technical service contracts, the strategy is that the optimal production target and workload of the project were determined by the return on investment, so as to ensure that the peak production and stable production periods meet the contract requirements.

Welcome Subscription '96 Environment Protection of Oil and Gas Fields

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